Electrode for electrostatic separation



Nov. 11, 1958 w. GROGG,- JR, ETAL 2,860,276

ELECTRODE FOR ELECTROSTATIC SEPARATION 2 Sheets-Sheet 1 Filed Dec. 2, 1955 FIG. 3

a mmm T. 2 m n mm W w W W P. R lwm .uwm/m E w M Y B Nov. 11, 1958 4 w. GROGG, JR.. r-rrm. 2,860,275

ELECTRODE FOR ELECTROSTATIC SEPARATION 7 Filed 090.2, 1955 2 Sheets-Sheet 2 FIG. 5

MIQRQAMPERES o s w as 20 25 so GRAMS EACH 0? DHPHENYLAMINE a BENZOPHENONIEVENTORS N I ms 3 (B WILLIAM GROGG, JR.,a

BYMELWN 2 WI BERG ATTOR N EYS lUnited States Patent ELECTRODE FOR ELECTROSTATIC SEPARATION William Grogg, Jr., Stow, and Melvin P. Wineberg, Copley, Ohio, assignors to The Quaker Oats Company, Chicago, 111., a corporation of New Jersey Application December 2, 1955, Serial No. 550,668

4 Claims. .(Cl. 313-351) The present invention relates to electrostatic separation. More particularly, the invention relates to an improved electrode of the comb orpoint type for use as the discharging electrode in electrostatic processes or apparatus.

An electrostatic separating apparatus utilizes the difference in dielectric capacity of materials to effect a separation of these materials. The materials being processed, examples of which are grain, coal and asbestos to name a few, are delivered by suitable feed means into the electrostatic field between a charging or charged electrode and a collecting or grounded electrode. One component of the material is preferentially attracted to (or repelled from) the chargedelectrode. The other component of the material is affected by the field to a lesser degree. Thus, by the use of a divider means and multiple banks of electrodes, it is possible to effectively separate the original material into two or more components. If a socalled low intensity electrostatic field is produced between the electrodes, then the separation is accomplished, as between the components, by the degree of attraction to the charged electrode. If a so-called high intensity" field is produced, then separation is achieved by the difference in degree of repulsion, as between component particles, from the charged electrode.

Separation of materials, whether due to the degree of repulsion or the degree of attraction, is achieved when a current is passed through the air gap between the charged and collecting electrode, such current differentially energizing particles of material passing in a stream through the relatively narrow electrostatic field.

The electrical energy in the electrostatic field is referred to as the "corona" or discharge current and is conventionally expressed in terms of microamperes per unit of electrode length. For example, a charged electrode in a "low intensity field may emit 60-180 microamperes/foot of electrode length. A "high intensity" electrode may emit 180-300 microamperes/foot of electrode length.

When conventional electrodes are used in electrostatic separation apparatus, a spark or are of sufiicently high intensity to ignite combustible dust or gas atmospheres may result when the resistance or insulation value of the air gap is lessened or reduced to a value approaching zero. This may occur for example when tramp metal reduces the gap distance, or high-moisture content material is passing through the air gap. The energy of the spark may be calculated according to the formula W==CV'/2, where W is the spark energy, C is the capacitance of the emitting electrode and V is the condenser voltage.

To achieve satisfactory separation, and yet reduce the possible energy level of a spark, it is necessary to reduce the capacitance (C) of the electrode. Heretofore, the circuitry of electrostatic separators has included various combinations of fixed value limiting resistors between the high voltage supply and the electrode.

The capacitance (C) of the electrode of the present invention is no more than the capacitance of each emission point as determined according to the formula -C-kA/d where k is the dielectric constant of the air gap,

"ice

A is the area of each individual needle or emission point, and d is the distance between the charged and collecting electrodes. The novel construction, as described hereinafter, including the use of a fluid conducting medium within the electrode proper, permits the continuous flow of a relatively high current to each individual needle of electrode; at the same time effectively isolating each needle one from the other, thus limiting any short circuit phenomena to the needles directly concerned and reducing the value of A in the above formula to an almost infinitestimal value.

It is an object of the present invention to provide a charged electrode of the comb or point type which will emit a corona current of sufficient amperage to differen tially energize materials in an electrostatic separation apparatus or process, and yet reduce the possible energy level of a spark or are to a value insuflicient to ignite combustible dust or gas atmospheres.

'It is another object to provide a charged electrode of the comb or point type which will permit a continuous flow of a relatively high current to each individual emission point.

Further it is an object to provide an electrode which can be short circuited without causing permanent damage thereto.

These and other objects of the invention will be apparent in view of the following detailed description thereof taken in conjunction with the attached drawings.

In the drawings:

Fig. 1 is a plan view, partially broken away, of an electrode according to the invention,

Fig. 2 is, a sectional view taken substantially on line 22 of Fig. 1,

Fig. 3 is a view, similar to Fig. 2, taken substantially on line 3-3 of Fig. 1, showing the electrode in its normal or operating position,

Fig. 4 is a schematic view of an electrostatic separation apparatus employing the improved electrode,

Fig. 5 is a plan view, similar to Fig. 1, showing an alternative construction of the electrode according to the invention, and

Fig. 6 is a graph of the amperage of a liquid filled electrode vs. composition of a solute mixture in a constant volume of solvent, as explained in moredetail hereinafter.

In a preferred form of the invention, the electrode comprises a hollow tube having a bus bar in the interior thereof and a series of spaced emitting needles extending through the wall of the tube opposite 'of the bus. Either end of the tube is sealed with a plug, an electrical connection to the bus being made through one of the end plugs. The tube is substantially filled with a liquid medium which conducts current from the bus to each of the individual emitting needles.

The electrode tube and end plugs are preferably constructcd of the methyl methacrylate polymers or resins. available under the trade name "Plexiglas" (from the Rohm & Haas Co., Philadelphia, Pa.) through other similar plastics or non-conductive materials possessing high mechanical strength and high dielectric properties could also be used.

The bus bar, connector and the emitting needles are preferably of stainless steel for purposes of corrosion resistance. However, it will be apparent that any metallic materials including copper, copper alloys or aluminum could-also be used.

The liquid medium conducting current from the bus to the emitting needles preferably comprises a mixture of solutes selected from the group consisting of diphenyl, diphenyl amine, thiodiphenylamine, pyridine, benzopbenone and diphenyl methane, in a solvent consisting essentially of a mixture of chlorinated phenyls and poly- P enyls. in polyhalogen substitution products of benzene, as described for example, in U. S. Patent No. 2,169,872. Clark et al., and available as a series of liquids under the trade name Pyranol (from The General Electric Co., chenec y. ew or lteferring to Fig. 4, a liquid filled electrode, indicated generally by the numeral 10, is mounted in a suitable structural member 11 by brackets 11a, in relation to a rotating grounded or collecting electrode 12 and a divider means 14. Material to be separated is supplied through a hopper 15 atop the member 11 and passes in a stream (S) through an electrostatic field (F) between the emitting electrode 10. and collecting electrode 12. The reject waste material (shown as dark particles) is preferentially energized to pass in a stream (R) to one side of the divider 1.4. The prime material is preferentially energized to pass in a stream (P) to the other side of the divider 14. The electrode 10 is connected by suitable wiring to the positive pole of a conventional rectifier or high voltage source 16, The collecting electrode 12 is connected with the negative pole of the high voltage source.

The electrode 10 consists of a preferably cylindrical medial portion or tube having a bus bar 21 extending the length thereof. The bus bar is secured by the small screws 22 to a rectangular support 23 extending inwardly from the tube wall. Opposite of the bus bar are a series of equally spaced (preferably 32 to the foot), needle-like elements 25 extending through the tube wall and positioned by a support 26 affixed to the exterior of the tube wall.

Either end of the tube 20 is affixed into sleeves 27 and 28. Affixed to the sleeve 27 is an end plug 29 having an aperture 30 through which a metallic connector 31 is threaded. Extending inwardly from the connector is a small diameter rod 32 which contacts the bus bar to complete the circuit within the electrode 10. The exterior portion of the connector 31 is surrounded by an insulating sleeve 33 aflixed to the end plug 29. A socket 34 is provided in the connector for the insertion of a banana plug 35, connected to wires leading to a high voltage source 16.

At the other end of the tube 20, the sleeve 28 has an aperture 36 through which the electrode is filled with the fluid conducting medium. This aperture is closed by an end plug 38 fastened to the sleeve by the. screws 39. Referring to Fig. 3, the tube 20- is not completely filled with the liquid 40. An air space. 40a is provided to allow for thermal expansion of the liquid.

Referring to Fig. 5, an alternative form of the electrode 1.0 utilizes a cylindrical bus bar 41 which extends through M 4 hs tt s A e l or a ket 44 preferably of neoprene, seals the bus bar within the fitting '43.' m. end of the rod 41. has a socket 45v therein to receiveaba'nanaplug 35, In this form of the invention, the fitting 43 and the. bus bar 41 are removed and the liquid 40 is poured therethrough to fill the electrode.

The liquid 40 is a conductive medium having substantial electrical resistance and containingasa solute mixtures of compounds selected from the group consisting of diphenyl, diphenylamine, thiodiphenylamine, pyridine, benzophenone, and diphenylmethane. The solvent is an oil available under the trade name "Pyranol," as described above. Referring to Fig. 6, a graphic representation of the current values per foot of. an electrode .using varying amounts of equal quantities of diphenylamine and benzophenone, in a fixcd quantity of Pyranol No. 1470, is presented. The lower left hand corner of the graph line shows that pure Pyranol. isnon-conductive. As the amount of solute is increased to four grams each (total 8 grams), the current has a value of approximately 114 microamperes. when 30gramseach of the solute aredissolved, the current value approximates 240 rnicroarn eres. As shown by the graph inFig. 6, a "low intensity field may be obtained by using from aboutv 2 grams to 14. grams, each, of the two solutes, resulting in a current of -180 microamps. A "high intensity" field, that is, a current of -240 microamps, may be obtained by using fron 1d to 30 grams, each, of the two solutes. Use Q: larger amounts than 30 grams each, of the two solute: does not result in an increase in amperage.

A tabular presentation of the test data upon which Fig. 6 is based is set forth in Table I; the solvent oil being 31 gms. in each instance, the voltage being 28,000 volts between the bus and the ground electrode.

Table I Current value in micronmpcres/loot ol electrode Table 11 Current value m1cro-, amperas/foot of electrode Grams each of pyridine and banwphenone Table III Ourrent.valuo tn microamperea/toot of Grams each of thlodlphenylsmlne and. dlphenylanuna elect: ode.

Table IV Current value in mlcroampares/toot oi Table V Current value Grams each of dlphenylmethane and dlphenylamlne in microemperes/toot oi electrode Table VI Current value Grams each of diphenyl and dlphenylomine tn mien omperes/toot of electrode Table VII Current value Grams each or pyridine and benzophenone in microamporos/ioot o1 electrode Table VIII Current value Grams each or dlphenyl and benzophenene in m1crovaruperes/foot:

of electrode While preferred forms of the invention have been shown and described it will be apparent that various changes and modifications could be made therein without departing from the spirit or scope of the invention. It will also be apparent that the present invention possesses certain other advantages not heretofore specifically referred to. For example, inconventional spark limiting circuits, it is necessary-to have up to as much as a 15,000 volt loss in the limiting circuit between the voltage source and the emitting electrode, in order to ensure low spark energy. Using the electrode of the invention (as shown schematically in Fig. 4) there is only a 5000 volt or less, loss between the power source 16 and the emitting electrode. Thus, a less expensive power source may be used to achieve the same amount of separation.

What is claimed is:

1. An electrode for use in electrostatic separation comprising a dielectric tube, end portions sealing said tube, a bus element located within and adjacent one side of said tube, electrical connections through one of said end portions contacting said bus, a series of spaced pointed emission elements extending through said tube from the interior thereof, and a liquid current conducting medium in said tube having substantial electrical resistance and contacting said bus element and said emission elements.

2. An electrode for use in electrostatic separation comprising a hollow dielectric member substantially filled with a current conducting fluid comprising a mixture of solutes selected from the group consisting of diphcnyl, diphenylamine, thiodiphenylamine, pyridine, benzophenone and diphenylmethane in a solvent consisting essentally of a mixture of chlorinated phenyls and poly-phenyls in polyhalogen substitution products of benzene, a bus element in the interior of said dielectric member, and a series of spaced pointed emission elements extending through the wall of said dielectric member.

3. An electrode for use in electrostatic separation comprising a dielectric tube, substantially filled with a current conducting fluid comprising a mixture of solutes selected from the group consisting of diphenyl, diphenylamine, thiodiphenylamine, pyridine, beuzophenonc and diphenylmethane in a solvent consisting essentially of a mixture of chlorinated phenyls and poly-phenyls in polyhalogen substitution products of benzene, end portions sealing said tube, a bus element located adjacent one side of said tube, electrical connections through one of said end portions contacting said bus element, and a series of spaced pointed emission elements extending through said tube from the interior thereof.

4. An electrode for use in electrostatic separation com prising, a hollow dielectric member, a bus element in the interior of said member, a series of spaced pointed emit ting elements extending through the wall of said member, and a liquid current conducting medium in said hollow member contacting said bus andemitting elements, said medium having the capacity to effectively isolate each emitting element one from the other.

' References Cited in the file of this patent UNITED STATES PATENTS 1,322,163 Conover Nov. 18, 1919 1,782,712 Chapman Nov. 25, 1930 2,239,695 Bennett Apr. 29, 1941 2,290,655 Thomay July 21, 1942 2,333,213 Slayter Nov.'2, 1943 

